Nearly one in four mammal species is in serious decline, mainly due to human activities. Hunting provides the most immediate threat to large animals such as rhinoceroses, elephants, tapirs, jaguars, and many primates. Between 1970 and 1992, black rhino numbers plummeted 96 percent due to hunting, and despite international agreements to protect species, few countries have resources to pursue poachers or the illegal trade in wildlife.

Mammals quickly become isolated when new roads, settlements, farms, or logging operations carve up their habitats. Many species, such as tigers and the giant panda live in populations peppered across heavily farmed, increasingly populated areas, few of which are large enough to sustain these animals well into the future.

The world's changing climate is a new challenge for mammal populations. The polar bear may be one of the first victims. In recent years, sea ice has melted earlier in the year in areas such as Canada's Hudson Bay, making it more difficult for the bears to hunt seals, their primary prey.